C.Hydrocephalus ex vacuo
- Refers to dilation of the ventricular system with a
compensatory increase in CSF volume secondary
to a loss of brain parenchyma, as may occur after
a. infarcts or
b. with a degenerative disease.
C. Herniation
- Intracranial pressure may increase by focal
expanding lesion or generalized edema..
- Because the cranial vault is subdivided by rigid
dural folds (falx and tentorium), a focal expansion
of the brain causes it to be displaced in relation to
these partitions
- If the expansion is sufficiently severe, herniation
will occur
- Herniations are named by .
a. Either the part of the brain that is displaced or
b. The structure across which it moves.
- The usual consequence of such displacement is
compromise of the blood supply to the "pushed"
tissue, resulting in infarction.
- This often leads to another round of swelling and
further herniation.
- Types of herniations:
1. Subfalcine (cingulate) herniation
- Expansion of a mass in the frontal or parietal lobe
will eventually result in herniation of ipsilateral
cingulate gyrus under the free edge of the falx to
produce selective displacement of the pericallosal
arteries away from the lesion and from the midline
- This may compromise circulation through the
pericallosal arteries ( branches of anterior cerebral
artery) and result in infarction of the parietal
parasaggital cortex , manifesting clinically as a
weakness or sensory loss in one or both legs
2. Tentorial (uncal) or uncinate gyrus herniationAny supratentorial expanding hemispheric mass
may produce herniation of the ipsilateral uncus
(tip and medial part of parahippocampal
gyrus)and medial part of the parahippocampal
gyrus medially and downwards through the
tentorial incisura
- This occurs most frequently when the mass is
located in the temporal lobe
- Consequences of temporal lobe displacement:
Uncal herniation
A. The ipsilateral oculomotor nerve compressed
between the free edge of the tentorium and the
posterior cerebral artery
1. At first the oculomotor nerve is flattened , and
compressed
2. Later, there will be hemorrhage in the oculomotor
nerve, and the resulting paralysis of the nerve
produces ptosis and dilation of the pupil ipsilateral
to the lesion
- Dilation of the pupil is the earliest consistent sign of
tentorial herniation and may occur before there is
any loss of consciousness
B. Compression of the cerebral peduncle (crus
cerebri)on the side of the mass lesion by direct
pressure from the herniating brain will result in
contralateral limb weakness
C. The posterior cerebral artery may also be
compressed, resulting in ischemic injury to the
territory supplied by that vessel, including the
primary visual cortex.
D. When the extent of herniation is large enough the
contralateral cerebral peduncle may be
compressed against the edge of the tentorium
and this may lead to its nfarction in the
this results in n hemiparesis ipsilateral to the side
of the herniation
NOTE:
- Because hemispheric lesions typically cause
contralateral weakness, this ipsilateral
hemiparesis can be a false localizing sign that
would suggest to the examiner that the patient
has a lesion in the opposite, unaffected
hemisphere
E. Duret hemorrhages .
- Progression of tentorial herniation is often
accompanied by hemorrhagic lesions in the in the
tegmentum of the midbrain and the tegmental
parts of the pons but not in the medulla
- Are linear or flame-shaped lesions
- The most likely mechanism of hemorrhage is
stretching and tearing of the central perforating
branches of the basilar artery that supply the rostral
brainstem leading to infarction or hemorrhage
- The presence of Duret hemorrhages implies a grim
prognosis
Durett hemorrhage
3. Central transtentorial hernion
- Occur in cases of :
a. Expanding frontal and parietal lesions
b. or bilateral chronic subdural hematoma
c. or diffuse brain swelling
• Both parahipocampal gyri will herniate
.
4.Tonsillar herniation (foramen impaction,
cerebellar cone)
- Refers to displacement of the cerebellar tonsils
through the foramen magnum.
- It occurs as an early complication of expanding
masses in the posterior cranial fossa but may also
occur with supratentorial space-occupying lesion
- The pathognomonic indication of this herniation is
hemorrhagic necrosis at the tips of the cerebellar
tonsils and a groove on the ventral surface of the
medulla where it is compressed against the anterior
border of foramen magnum
- This pattern of herniation is life-threatening
Tonsillar herniation
III. CNS Tumors
- About half to three-quarters are primary tumors,
and the rest are metastatic.
- Tumors of the CNS make up a larger proportion of
cancers of childhood, accounting for as many of
20% of all tumors.
- CNS tumors in childhood differ from those in adults
both in histologic subtype and location.
- In childhood, tumors are likely to arise in the
posterior fossa, while in adults they are mostly
supratentorial.
- Tumors of the nervous system have unique
characteristics that set them apart from neoplastic
processes elsewhere in the body.
a.These tumors do not have detectable premalignant
or in situ stages comparable to those of carcinomas
b.Even low grade tumors may infiltrate large regions
of the brain, thereby leading to serious clinical
deficits and poor prognosis , non-resectability, and
poor prognosis.
c.The anatomic site of the neoplasm can influence
outcome independent of histologic classification
due to local effects
a. A benign meningiomas may cause cardio
respiratory arrest from compression of the
medulla
b. Brain glioma may be non- resectable
- Even the most highly malignant gliomas rarely
spread outside the CNS
- Some tumors may infiltrate the subarachnoid
space
- Medulloblastoma may spread to distant sites
I. Gliomas
- Gliomas are tumors of the brain parenchyma that
are classified the basis of their resemblance to
different types of glial cells.
- The major types of tumora in this category are:
A. Astrocytomas,
B. Oligodendrogliomas,
C.Ependymomas
A. Astrocytoma :
- Several different categories of astrocytic tumors
are recognized, the most common being:1.Diffuse ( infiltrative)
2.Pilocytic astrocytomas.
1. Diffuse Astrocytoma :
- Account for about 80% of adult primary brain
tumors.
- Most frequent in the fourth through sixth decades.
- Usually are found in the cerebral hemispheres
- The most common presenting signs and
symptoms are:
a. Seizures,
b. Headaches
c. Focal neurologic deficits related to the anatomic
site of involvement
- They show a spectrum of histologic differentiation
that correlates with clinical course and outcome
- On the basis of histologic features, they are
divided into three groups
a.Well-differentiated astrocytomas(WHO grade II/IV:
- Symptoms can be static or progress only slowly
during a number of years but at some point
progress
- The mean survival is more than 5 years.
- Eventually, patients suffer rapid clinical
deterioration .
- These tumors are poorly defined, infiltrative
tumors that expand and distort invaded brain
without forming a mass
Microscopic appearance:
a. A mild to moderate increase in the number of
astrocytic nuclei with mild nuclear pleomorphism
b. An intervening GFAP-positive astrocytic cell
processes that give the background a fibrillary
appearance
c. The transition between neoplastic and normal
tissue is indistinct,
d. Tumor cells can be seen infiltrating normal tissue
at some distance from the main lesion.
b.
1.
2.
3.
Anaplastic astrocytomas (WHO GRADE III)show:
Regions that are more densely cellular
The cells have greater nuclear pleomorphism
Increased mitoses are often observed (The most
important feature).
AnaplasticAstrocytoma
Astrocytoma(WHO grade III)
Anaplastic
(WHO grade III)
c. Glioblastoma (WHO grade IV)
- It has a histologic appearance similar to
anaplastic astrocytoma with the additional
features of:
a. Pseudopalisading necrosis
b. and /or b. Microvasular proliferation
Note
- Glioblastomas have abnormal vessels that are
"leaky" and will show contrast enhancement with
imaging studies
• Glioblatomas are either:
1. Primary
- The patients develop it from the start
- Is the most common type of glioblastoma
2. Secondary
- Progress from lower grades
Note : Once the histologic features of glioblastoma
appear, the prognosis is very poor; with treatment(
resection , radiotherapy , and chemotherapy), the
median survival is only 15 months
Glioblastoma (WHO grade IV)
Glioblastoma
• Genetic Changes in astrocytomas
1. In low grade astrocytomas(grade II)
- Mutations that alter the enzymatic activity of two
isoforms of the metabolic enzyme isocitrate
dehydrogenases(IDH1 and IDH2)and this genetic
change differentiates this tumor from gliosis and
pilocytic astrocytoma
2. In glioblastomas
- Loss of function mutation in p53 and Rb tumor
suppressor pathway
2. Pilocytic astrocytomas WHO grade I
Are relatively benign tumors
Typically occur in children and young adults
Are usually located in the cerebellum
Other locations:
a. Floor and walls of the third ventricle,
b. The optic pathways(called optic glioma)
c. Spinal cord and occasionally the cerebral
hemispheres.
• Note: Infatile pilocytic astrocytoma is called
pilomyxoid astrocytoma and it is grade II typically
located in the hypothalamus
Morphology of pilocytic astrocytoma
Gross:
- Well circumscribed
- Is often cystic, with a mural nodule in the wall of
the cyst
Microscopically, the tumor is composed of
a. Hypercellular areas composed of bipolar
astrocytes with with long, thin "hairlike "
processes that are GFAP positive
b. Hypocellular areas formed of microcysts.
c. Rosenthal fibers
d. Eosinophilic granular bodies,
e. Necrosis and mitoses are absent.
• Genetically Pilocytic astrocytomas don’t show
mutations in IDH1 and IDH2
Pilocytic astrocytoma
Pilocytic astrocytoma
- Tumors that appear on MRI as cyst containing a
nodule are:
a. Pilocytic astrocytoma
b. Ganglioglioma
c. Pleomorphic Xantho astrocytoma
QUIZ 2
• What is the nucleus that is located
beneath the anterior commissure in
the basal forebrain and rich in
acetylcholine